The present invention is related to polymeric fibers, and more particularly to polymeric fibers formed of a nanocomposite material.
Synthetic polymers have been widely used in the production of fibers, films, molded articles, and the like. Common thermoplastic polymers used in the production of these and other products include polyolefins, polyesters, and polyamides, among others.
Typically one or more additives can be added to the polymer melt prior to extrusion to improve specific properties. For example, an anti-oxidant is typically added to polypropylene prior to extrusion to minimize degradation. As another example, fire retardant fillers can be added to control polymer flammability. Other fillers used in the production of polymeric articles include titanium oxide (TiO2), kaolin, pigments, carbon black, and the like.
While the addition of these and other fillers can improve a particular property of the resultant product, there can be problems associated with the use of such fillers. For example, the presence of a filler may improve one property of the end product while concurrently diminishing or adversely impacting another property. As an example, certain fillers can improve the flame retardant property of a polymeric article. However, high levels of loading are typically required to impart the desired degree of flame resistance. This in turn can alter the mechanical properties of the product, such as mechanical robustness.
Still further, use of fillers in the production of polymeric articles can cause processing problems. For example, fillers present in an extruded polymer can pose filter and capillary plugging hazards. In addition, the surface properties of the end product can be compromised, creating a rough, abrasive surface, instead of a smooth surface.
The present invention provides fibers formed of a polymeric nanocomposite material. Nanocomposite materials generally include a polymer having nanosized inorganic platelet particles dispersed therein, e.g., platelet particles having a nanometer size range in at least one dimension thereof.
The size of the particles can vary depending upon the material used to make the same. Generally the platelet particles can be described as modified clay materials with very high aspect ratios (the ratio of the object""s width to its thickness). Thus the particles may also be described as having a very minimal thickness relative to their length. Generally such particles have an average diameter between about 10,000 xc3x85 and about 50 xc3x85, and an aspect ratio length/thickness ranging from about 1000 to about 1. The particles typically have an average thickness of less than or about 20 xc3x85, and preferably an average thickness of less than or about 10 xc3x85. This is in contrast to conventional filler materials, such as kaolin, titanium dioxide, carbon and the like, which have much larger sizes and typically are roughly or substantially spherical in shape.
The resultant fibers can be monocomponent fibers. Alternatively the fibers of the invention can be multicomponent fibers, which include at least two structured polymeric components. For multicomponent fibers of the invention, generally at least one polymer segment includes a nanocomposite material, while at least one other polymeric segment includes a different nanocomposite material and/or other fiber forming polymeric material, which may or may not include nanoparticles.
The inventors have found that the fibers of the invention can exhibit several advantageous properties, as compared to conventional fibers formed without a nanocomposite material and/or formed with conventional fillers. Further, these benefits can be achieved at relatively low loading levels of the nanosized platelet particles. For example, the resultant fibers can exhibit enhanced strength, e.g., tensile yield strength and flexural modulus, as compared with fibers which are free of the nanocomposite material, or which contain conventional powdered fillers such as unexfoliated clay, silica or carbon black. Indeed, in contrast to the present invention, the use of such conventional fillers in fiber production typically degrade fiber properties such as tensile strength, tensile modulus and the like. The fibers of the invention can also exhibit improved stiffness and heat resistance, and decreased moisture absorption, flammability, and permeability, as compared to fibers prepared without filler and/or with conventional fillers.
Still further, the present invention can provide processing advantages. The nanosized nature of the platelet particles can reduce processing problems associated with the extrusion and spinning of conventional filled polymers into fibers, such as filter and capillary plugging.